Heavy doors, such as those used on walk-in refrigerators, are often mounted to jambs by butt mounted riser type hinges which lift the door when it is swung open, and which use gravity to assist in the closing of the door. A butt mounted hinge is one which has two barrels mounted one above the other. Each barrel has a mounting flange laterally extending therefrom, and generally, the flanges are side by side in the based position of the hinge, in the space between the door and the jamb. The flange of one barrel is secured to the door edge and the flange of the other barrel is secured to the jamb. With this configuration, flange mounting screws are inaccessible when the door is in its closed position. Therefore when closed and locked, the door may not be opened by merely removing the hinge. This provides a high degree of security. The butt mounted hinge is also aesthetically pleasing, inasmuch as when the door is closed the hinge flanges are concealed.
A riser hinge is a hinge which incorporates a means for raising the door as it is swung open. Typically this is in the form of a camming arrangement in which the barrel of the hinge mounted to the door rides up a camming surface as the door swings open, thereby lifting the door. This feature is desirable for two reasons. Firstly, as the door is swung open the clearance between the bottom of the door and the floor is increased, so that door operation is not hindered by small objects resting on the floor or floor variances in its path. The problem of floor clearance is important where the refrigerator floor and the adjoining floor are at the same level since to assure a good seal the door must fit tightly against the floor when fully closed, yet have ample clearance when being swung open. Secondly, once the camming system has been actuated by opening the door, the door may be automatically closed upon being let go, with the weight of the door itself actuating the camming system in the reverse direction.
Riser hinges are also usually made of two parts that have axially aligned metallic barrels from which mounting flanges laterally extend. Mounted in each barrel is a cylindrical camming element made of a smooth, low friction material such as a hard plastic. Their mutually confronting ends are bevelled. Thus, as the barrel of the part mounted to the door is rotated, its bevelled camming element is driven upwardly upon the bevelled end surface of the other camming element, thereby causing the door to rise. Exemplary of a hinge which is both butt mounted and riser as that shown in U.S. Pat. No. 3,545,032.
A problem long associated with this type of hinge is that not only is there frictional contact on the bevelled cam surfaces but also on the cylindrical surface of one of the camming elements as it rises or falls and simultaneously rotates within a stationary barrel. This sliding contact movement of a relatively soft camming element and relatively hard metallic barrel causes the side wall of the cam element to become worn and deformed, thus it must be replaced from time to time. The weight of the door also causes a bending moment on the hinge inasmuch as the center of gravity of the door is laterally offset from the axis of the hinge. This bending moment in turn increases the frictional pressure between the cam element side wall and that of the barrel, thereby increasing the wear of the cam follower.
It thus is seen that a need remains for a heavy duty butt mounted riser hinge which alleviates problems associated with those of the prior art. It is to the provision of such therefore that the present invention is primarily directed.